The present invention generally relates to an implantable cardiac stimulation device. The present invention more particularly relates to such a device and a method, which discriminates between noise sensing and arrhythmia detection.
Implantable cardiac stimulation devices are well known in the art. They include implantable pacemakers which provide stimulation pulses to a heart, which would normally or otherwise beat too slowly or at an irregular rate, to beat at a controlled normal rate. They also include defibrillators which detect when the atria and/or the ventricles of the heart are in fibrillation and apply cardioverting or defibrillating electrical energy to restore the heart to a normal rhythm. Implantable cardiac stimulation devices may also include the combined functionalities of a pacemaker and a defibrillator.
As is well known, implantable cardiac stimulation devices sense cardiac activity for monitoring the cardiac condition of the patient in which the device is implanted. By sensing the cardiac activity of the patient, the device is able to provide cardiac stimulation therapy when it is required.
Unfortunately, noise within the device sensing channel bandwidth can interfere with the sensing function. In a pacemaker, for example, noise can be mistaken by the device for a legitimate cardiac event causing stimulation inhibition. This can lead to long periods of a systole. In an implantable defibrillator, noise can cause mistaken diagnosis of fibrillation resulting in inappropriate therapy delivery.
Unneeded defibrillation therapy to the atria can cause unwarranted discomfort to a patient, and hence should be avoided. However, unneeded defibrillation therapy to the ventricles can be much worse. Generally, patients suffering from an episode of ventricular fibrillation are rendered unconscious before therapy is delivered. Even though the defibrillation shocks are of relatively high energy, to assure defibrillation, they are not felt by the patient. However, if ventricular fibrillation is inappropriately detected and the patient is conscious when the unneeded therapy is delivered, the therapy could be traumatic to the patient. Even worse, inappropriate shocks can induce ventricular fibrillation to create a potentially life threatening situation. As a result, it is most desirable, if not essential, that such unnecessary ventricular defibrillation therapy or shocks be avoided. The present invention provides an implantable cardiac stimulation device and method capable of discriminating between sensed noise and cardiac tachyarrhythmias to avoid the delivery of unnecessary defibrillation therapy.
The present invention provides an implantable cardiac stimulation device and method, which discriminates between sensed noise and cardiac arrhythmias. The noise discrimination contemplated by the present invention is based upon the fact that noise interference, sensed at one location of the heart will be closely correlated to the noise from the same source sensed at another distant location of the heart. However, during an arrhythmia, such as fibrillation, localized cardiac electrical activity sensed at one location of the heart will not find good correlation with localized cardiac electrical activity sensed at the other distant location of the heart.
In accordance with the broader aspects of the present invention, a first sensing circuit senses electrical activity at a first location of the heart to generate a first signal and a second sensing circuit senses electrical activity at a second location of the heart to generate a second signal. The first and second locations are spaced apart and may be in a common chamber or in respective different corresponding chambers such as the right atrium and the left atrium or the right ventricle and the left ventricle. As used herein, the recitation of xe2x80x9cin a chamberxe2x80x9d is meant to include sensing within a given chamber as well as sensing from a location closely adjacent to and in electrical contact with the given chamber. Hence, the sensing of electrical activity in the left ventricle or in the left atrium includes sensing electrical activity with an electrode positioned in the coronary venous system of the heart adjacent the respective chamber.
The first and second signals are compared by a comparison circuit as implemented, for example, in a processor, to provide a comparison factor. A control circuit determines from the comparison factor if noise is being sensed or if an arrhythmia is being sensed.
If it is determined that noise is being sensed, the implantable cardiac stimulation device may be caused to revert to a noise reversion mode. However, if it is determined that an arrhythmia is being sensed, the implantable cardiac stimulation device may be caused to change operating state to enter a therapy mode of applying cardioversion therapy to the subject chambers. The cardioversion therapy may include, for example, high or low energy defibrillation therapy or anti-tachyarrhythmia pacing therapy. The therapy mode may first include arrhythmia confirmation by an arrhythmia detector before defibrillation or cardioversion.